1. Field of the Invention
This invention relates to a vibration wave driven type motor apparatus for effecting various kinds of highly accurate constant speed feeding, positioning, etc. with a vibration wave driven motor as a drive source.
2. Related Background Art
A vibration wave driven type motor is such that a vibration member in which a travelling vibration wave is formed and a member, for example, a rotor, which is in pressure contact with the vibration member are frictionally driven by the travelling vibration wave and moved relative to each other. The motor has the characteristic that stable rotation is obtained in a low speed, and also has the feature that because the vibration member and the driver held in a pressed state, the relative movement thereof is stopped as soon as the supply of driving electric power to the vibration member is cut off. Therefore, it has been proposed to use a vibration wave driven type motor as a drive source for an apparatus which requires highly accurate drive control, such as a paper feeding mechanism in a printer or a driving mechanism for the printing head of a printer. Also, in a camera, a vibration wave driven type motor is used for driving a focusing lens.
On the other hand, the vibration wave driven type motor, as is known, is designed such that a metallic elastic member formed, for example, into a ring shape and having a piezo-electric element adhesively secured thereto is used as a vibration member and an AC voltage is applied to two groups of driving phases in the piezo-electric element, whereby a travelling vibration wave (wavelength .lambda.) is formed in the elastic member by the combination of standing waves which are 90.degree. out of phase with each other, and the two groups of driving phases are provided at locations positionally deviating from each other by odd number times .sub.4.sup..lambda., and the AC voltage applied to these driving phases has a time phase of 90.degree..
On the other hand, a member urged against the elastic member of the vibration member is frictionally driven by a travelling vibration wave formed in the elastic member and, therefore, is adapted to be urged against the elastic member with a friction member interposed therebetween.
In order to obtain highly accurate relative movement, the portion of contact between the elastic member and the friction member is formed into a surface having a highly accurate flatness, and the squareness of the surface of the portion of contact to the rotary shaft of the motor is formed with high accuracy so that there may be no irregularity of surface pressure.
However, a high-degree machining technique and a long machining time are required to finish the contact surface of the elastic member and the friction member of the vibration wave driven motor into a highly accurate flat surface, and this leads to a high cost.
So, if an attempt is made to shorten the machining time and reduce the cost, the degree of flatness will become bad. In particularly in lapping work, an increase in pressure force for the purpose of shortening the time would tend to cause a so-called two-bend phenomenon in which the degree of flatness of the elastic member and the friction member is bent into two, and this may result in irregular surface pressure during relative movement, which in turn may cause irregular rotation.
Also, the irregular surface pressure increases the influence of the phenomenon that the amplitude of the travelling vibration wave fluctuates depending on the eccentricity of a slit formed in the elastic member, the eccentricity of the rotor and the irregularity of the travelling vibration wave, i.e., at what location on the elastic member the antinode of the travelling vibration wave lies, and each portion driver by the vibration wave driven motor vibrates. Thus control has become difficult in some cases.